This invention relates to flow control valves, and more particularly to a flow control valve which can be used to regulate or stop the flow of steam or other high temperature fluid. The invention has broad application in fluid flow control, but is particularly useful as a thermally responsive fluid valve, and has particular utility in the elimination of condensate from the steam system in an apparatus such as a steam turbine, a steam engine, a steam heating system for a building, a steam autoclave, a steam-operated humidifier, steam-operated chemical processing equipment, and other equipment utilizing steam as a source of heat, pressure or humidity.
To achieve optimum operating efficiency in such equipment, it is desirable to eliminate condensate to the extent possible. In order to do this automatically, various devices known as steam traps have been devised. In general, a thermostatic steam trap, which is situated at a suitable location in a steam line, detects the presence of condensate by sensing the temperature of the condensate, which is lower than that of steam. When condensate is detected, an aperture in the steam trap opens to discharge the condensate. The discharged condensate is replaced by steam, which, by virtue of its higher temperature, causes the aperture to reclose. As a result, the steam trap discharges condensate automatically without allowing significant amounts of steam to escape.
Most thermostatic steam traps currently in use are either bimetallic disc steam traps or bellows-type steam traps. As the name implies, the first type of steam trap utilizes a bimetallic disc as a temperature sensing element. A stack of bimetallic discs is disposed inside a housing having an inlet connected to a steam system, and a valve is arranged to exhaust fluid from the steam system as the fluid flows through the housing past the stack of bimetallic discs. The stack mechanically moves a valve element toward and away from a valve seat, depending on the temperature of the fluid inside the housing. The bellows type steam trap utilizes a fluid-filled bellows, instead of a stack of bimetallic discs, as a temperature sensing element.
In both cases, when the temperature sensing element is exposed to steam, the temperature of the steam causes the valve element to move, in the closing direction, into contact with the valve seat, while the lower temperature of condensate accumulating in the sensor housing causes the valve to move away from the seat in order to discharge the condensate, until the condensate is exhausted and the sensor is once again exposed to steam, whereupon the sensor once again causes the valve element to close.
The temperature of saturated steam increases with increasing pressure according to a well-defined relationship known as the steam curve. Likewise, the temperature of the condensate in a closed system increases with increasing steam pressure. Accordingly, in an ideal steam trap, the temperature at which the steam trap discharges condensate should be higher when the steam pressure is high, and lower when the steam pressure is lower. In a conventional steam trap utilizing a stack of bimetallic discs as the temperature sensor, a higher steam temperature causes the sensor to exert a greater closing force on the valve element, while at the same time, the higher pressure exerts a force on the valve element tending to move the valve element in the opening direction. Therefore, in a well-designed bimetallic disc steam trap, a balance is achieved, by which the device follows the steam curve, discharging condensate as it accumulates, regardless of the steam pressure in the system.
A thermostatic bellows steam trap functions in a similar manner. The fluid within the bellows expands with increasing temperature, urging the valve element in the closing direction, while increasing pressure acts to compress the bellows. The oppositely acting effects of temperature and pressure, when appropriately balanced, cause the device to discharge condensate at a temperature near the saturated steam temperature at any pressure.
These conventional steam traps have various limitations and disadvantages, including high manufacturing cost, large size, difficulty of adjustment, and limited service life.
An object of this invention is to provide a simple and effective steam trap that exhibits one or more of the following advantages over conventional steam traps: lower cost, compactness, ease of adjustment, and long service life.
It is also an object of the invention to provide a simple and effective temperature-responsive fluid valve for use in a broad range of applications using steam and other fluids.
Still another object of the invention is to provide a simple and effective fluid control valve for use in various fluid flow control applications in which temperature responsiveness is not required.
The valve in accordance with the invention comprises a housing having a tubular side wall and two end walls. A first end wall at a first end of the side wall, defines one end of an internal space. A second end wall at the opposite or second end of the side wall, has a centrally located aperture arranged to provide fluid communication between the internal space and the exterior of the housing. At least one passage extends through the side wall at a location adjacent the second end wall, and is arranged to provide fluid communication between the exterior of the housing and the internal space. Preferably a plurality of such passages is provided. A valve element substantially fills all of the internal space except for a portion thereof adjacent the second end of the side wall. At least the part of the valve element which contacts the tubular side wall of the housing is composed of an elastomer. In some applications, the entire valve element can be composed of elastomer. In others an expansible wax can be incorporated in a space inside the elastomer. In still others, a rigid element can be embedded in the elastomer at a location such that the rigid element, rather than the elastomer, engages a valve seat.
The valve seat is in the form of a boss surrounding the centrally located aperture of the second end wall and extending toward the first end wall. By virtue of its elastomeric content, the valve element is deformable from a first condition in which it is spaced from the seat and allows fluid communication between the one or more passages in the side wall and the aperture in the second end wall, to a second condition in which it engages the seat, thereby closing the aperture and preventing fluid communication between the passages in the side wall and the aperture.
The temperature coefficient of expansion of the elastomer is preferably in the range from 0.01%/xc2x0 F. to 0.2%/xc2x0 F., and in a preferred embodiment of the invention, the valve element is composed of a plurality of cylinders disposed in a stack in the housing, in coaxial relationship with the tubular side wall of the housing. The use of a plurality of cylinders simplifies molding of the elastomer, and also makes it possible to vary the characteristics of the valve member by combining different cylinders. Thus, one cylinder might incorporate a thermally expansible wax or other composition, or a rigid, seat-engaging element, while the other is formed entirely of elastomer. In other cases, both cylinders can be composed entirely of elastomer
The side wall is preferably formed of metal, and the elastomer is in contact with the side wall, so that heat is rapidly conducted through the side wall to and from the elastomer.
In a preferred embodiment, the first end wall comprises a metal plate secured to the side wall and in contact with the elastomeric member. The operating temperature of the valve can be set by preliminarily bending the metal plate into a dish shape, so that it has a convex face in contact with the valve member. The extent to which the plate is bent determines the temperature at which the valve closes at a given pressure. A similar adjustment can be effected by other means, for example, a plunger adjustable by a screw or by a handwheel.
The side wall of the housing may be provided with a shoulder formed adjacent its first end, and the metal plate can be held against the shoulder by crimping a thin-walled ring projecting from the shoulder.
To retain the valve element in proper position in the tubular housing, another shoulder is formed on the side wall inside the internal space, adjacent, but spaced from, the second end, and facing the first end wall. The valve element has an end surface facing the second end wall, the end surface having a peripheral area in engagement with the shoulder so that at least the peripheral area is retained in spaced relationship with the second end wall. Because the outer part of the valve element is formed of elastomer, the valve element can deform and approach the seat despite the fact that the periphery of its end surface is immobilized by engagement with the shoulder.
In a preferred embodiment of the valve, the housing includes a passage connecting the aperture with the exterior of the housing. This passage has a central portion narrower than the aperture, a connecting portion converging from the aperture to the central portion, and a diverging portion connecting the central portion to the exterior of the housing.
The side wall has an exterior face and an interior face, and each passage extending through the side wall at a location adjacent the second end wall has an outer end opening in the exterior face of the side wall, an inner end opening in the interior face of the side wall, and a tapered portion extending through a portion of the side wall between the inner and outer end openings, the tapered portion having a wider end toward the exterior of the housing and a narrower end toward the interior of the housing. A space, between the boss surrounding the central aperture and the side wall, provides a cross-section to the flow of fluid larger than the total of the cross-sections of the narrower ends of the tapered portions. Each passage extending through the side wall at a location adjacent the second end wall has an inner end opening in the interior face of the side wall directly opposite to the boss, and the space between the boss and the side wall provides a larger cross-section to the flow of fluid than the space between the boss and the elastomeric element when the elastomeric element is spaced from the boss to allow fluid communication. The centrally located aperture in the second end wall of the housing also has a cross-section larger than said space between the boss and the elastomeric element. Consequently, in the preferred embodiment, there are three separate stages in which the flow cross-section converges and then diverges: one at the location of the openings in the side wall; another at the location at which the elastomeric member approaches the valve seat; and a third in the exit passage beyond the aperture in the second end wall.
The exterior face of the side wall preferably has an annular recess in a portion adjacent its second end, and the passages extend through the part of the side wall having the annular recess. A filter screen spanning the recess is therefore spaced from the openings of these passages.
The second end wall may have an extension with external threads for mounting the valve.
For adjustment of the size of the portion of the internal space adjacent the second end of the side wall, a plunger may be arranged so that it extends through an opening in the first end wall, the plunger having an end in contact with, and exerting a compressive force on, the valve element.
The valve element may composed in part of an elastomer, and include a thermally expansible material, having a coefficient of expansion greater than that of the elastomer, and situated in an interior space within the valve element and surrounded by part of the elastomer.
The valve element may include a rigid element in elastomer, and arranged so that the part of the valve element which engages the seat is part of the rigid element.
As will be apparent from the following detailed description, the valve structure, comprising a valve element, composed at least in part of an elastomer, in a tubular enclosure, not only provides a compact and reliable steam trap operable over a wide range of pressures, but may also be utilized advantageously in other applications in which a temperature-responsive fluid valve is required, and also in other fluid flow control applications in which temperature responsiveness is not required.
Other objects, details and advantages of the invention will be apparent from the following detailed description when read in conjunction with the drawings.